It (#99, #98) holds in the plastic plate (#97) under the shell dies at that post. The plate creates a removable floor in the crosshead so the dies could be removed from the older solid aluminum turrets. It's redundant in the new loaders with the Grivory turrets and the die removal system.<center>
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The one to the left of station 1 under the primer feed adjusts the height of the primer post after the allen screw is loosened.<center>
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I suppose you're speaking of the one on the primer feed apparatus, under the coil spring. It's an adjuster for setting seating depth of the primers, along with the set screw just under it. If your primers are where you want them, this is a good adjustment to avoid messing with.